Browsing by Author "Lindsay, R."
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Item Calibration of germanium detectors for applications of radiometric methods in South Africa.(University of the Western Cape, 2001) Maleka, P.P; Lindsay, R.; de Meijer, R. I.AII materials that are radioactive emit characteristic gamma-radiation. Natural radioactivity can be used in heavy minerals exploration and processing, as well as in understanding sediment transport. processes in coastal zones [Dem97][Dem98]. Differences in radionuclide concentrations between minerals, allows the mineral species to be identified and quantified by the activity concentrations of a011, 23216 and 238U using a technique called radiometric fingerprinting [Dem97]. A" important tool to determine sediment transport rates along the coastline is by the MEDUSA technology developed and tested at the Kernfysisch Versneller Instituut (KVI) [Dem98]. The data from the MEDUSA (Multi-Element Detector system for IJnderwater Sediment Activity) system needs to be calibrated first in the laboratory before field measurements can be converted to useful data. The National Accelerator Centre (NAC) is setting up a radiometric laboratory to do this by means of a high-resolution germanium detector used under low-background conditions and constant geometry.Item Characterisation of natural radioactivity in Karoo Basin groundwater prior to shale gas exploration(University of the Western Cape, 2017) Botha, Ryno; Lindsay, R.; Newman, R.T.; Maleka, P.P.The prospect of unconventional shale-gas development in the Karoo Basin (South Africa) has created the need to obtain baseline data on natural radioactivity in Karoo groundwaters. The Karoo Basin groundwater radiological baseline developed through this study could serve as a reference to research potential future radiological contamination effects due to hydraulic fracturing. The major naturally occurring radioactive material (NORM) studied was radon (222Rn), in particular in-water activity concentrations; however, supplementary radium (226Ra and 228Ra) in-water activity concentrations and uranium (238U) in-water concentrations measurements were also made. A total of 53 aquifers across three provinces were sampled for groundwater and measured, with three measurement series from 2014 to 2016. The aquifers were categorized as shallow, mixed, or deep source. The radon-in-water baseline of the Karoo Basin can be characterised by a minimum of 0.6 ± 0.9 Bq/L, a maximum of 183 ± 18 Bq/L and mean of 41 ± 5 Bq/L. The radon-in-water levels from shallow sources (with water temperature < 20 °C) were systematically higher (40 Bq/L) than for deep sources (with water temperature > 20 °C). The natural fluctuations in radon-in-water levels were predominantly associated with shallow aquifers compared to almost none observed in the deep sources. The uranium in-water baseline can be characterised by a minimum of below detection level, a maximum of 41 μg/L, and the mean of 5.10 ± 0.80 μg/L. Similar to radon-in-water levels, uranium in-water levels for shallow sources were systematically higher than for deep sources. The limited (six aquifers) radium (228Ra and 226Ra) in-water activity-concentration measurement results were very low, with a maximum of 0.008 Bq/L (226Ra) and 0.015 Bq/L (228Ra). The 228Ra/226Ra ratio baseline were characterised by a minimum of 0.93, a mean of 3.3 ± 1.3, and a maximum of 6.5. The radium isotopes’ activity concentration ratio is an isotopic tracer for hydraulic fracturing wastewater. Pollution and contamination (radiological), due to unconventional shale gas development, in water resources has been noticed in the Marcellus Basin (United States). Consequently, developing and improving continuous baseline monitoring are of importance to study the environmental radiological effect of hydraulic fracturing.Item Determination of natural radioactivity concentrations in soil: a comparative study of Windows and Full Spectrum Analysis(University of the Western Cape, 2004) Maphoto, Katse Piet; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of ScienceIn this study, two methods of analysing activity concentrations of natural radionuclides (U, Th and K) in soil are critically compared. These are the Window Analysis (WA) and Full Spectrum Analysis (FSA). In the usual WA method, the activity concentrations are determined from the net counts of the windows set around individual γ-ray peaks associated with the decay of U, Th and K. In the FSA method, the full energy spectrum is considered and the measured spectrum is described as the sum of the three standard spectra (associated with U, Th and K, respectively), each multiplied by an unknown concentration. The concentrations are determined from the FSA and correspond to the activity concentrations of U, Th and K in the soil. The standard spectra derived from separate calibration measurements using the HPGe detector, represents the response of the HPGe to a Marinelli sample beaker containing an activity concentration of 1 Bq/kg.Item Determination of the photopeak detection efficiency of a HPGe detector, for volume sources, via Monte Carlo simulations(University of the Western Cape, 2005) Damon, Raphael Wesley; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of ScienceThe Environmental Radioactivity Laboratory (ERL) at iThemba LABS undertakes experimental work using a high purity germanium (HPGe) detector for laboratory measurements. In this study the Monte Carlo transport code, MCNPX, which is a general-purpose Monte Carlo N − Particle code that extends the capabilities of the MCNP code, developed at the Los Alamos National Laboratory in New Mexico, was used. The study considers how various parameters such as (1) coincidence summing, (2) volume, (3) atomic number (Z) and (4) density, affects the absolute photopeak efficiency of the ERL’s HPGe detector in a close geometry (Marinelli beaker) for soil, sand, KCl and liquid samples. The results from these simulations are presented here, together with an intercomparison exercise of two MC codes (MCNPX and a C++ program developed for this study) that determine the energy deposition of a point source in germanium spheres of radii 1 cm and 5 cm. A sensitivity analysis on the effect of the detector dimensions (dead layer and core of detector crystal) on the photopeak detection efficiency in a liquid sample and the effect of moisture content on the photopeak detection efficiency in sand and soil samples, was also carried out. This study has shown evidence that the dead layer of the ERL HPGe detector may be larger than stated by the manufacturer, possibly due to warming up of the detector crystal. This would result in a decrease in the photopeak efficiency of up to 8 % if the dead layer of the crystal were doubled from its original size of 0.05 cm. This study shows the need for coincidence summing correction factors for the gamma lines (911.1 keV and 968.1 keV) in the 232Th series for determining accurate activity concentrations in environmental samples. For the liquid source the gamma lines, 121.8 keV, 244.7 keV, 444.1 keV and 1085.5 keV of the 152Eu series, together with the 1173.2 keV and 1332.5 keV gamma lines of the 60Co, are particularly prone to coincidence summing. In the investigation into the effects of density and volume on the photopeak efficiency for the KCl samples, it has been found that the simulated results are in good agreement with experimental data. For the range of sample densities that are dealt with by the ERL it has been found that the drop in photopeak efficiency is less than 5 %. This study shows that the uncertainty of the KCl sample activity measurement due to the effect of different filling volumes in a Marinelli beaker is estimated in the range of 0.6 % per mm and is not expected to vary appreciably with photon energy. In the case of the effect of filling height on the efficiency for the soil sample, it was found that there is a large discrepancy in the trends of the simulated and experimental curves. This discrepancy could be a result of the use of only one sand sample in this study and therefore the homogeneity of the sample has to be investigated. The effect of atomic number has been found to be negligible for the soil and sand compositions for energies above 400 keV, however if the composition of the heavy elements is not properly considered when simulating soil and sand samples, the effect of atomic number on the absolute photopeak efficiency in the low energy (< 400 keV) region can make a 14 % difference.Item Development and study of a Thoron (Rn-220) standard source(University of Western Cape, 2019) Elhag, Elmughera Hussein Salim; Lindsay, R.Thoron Rn-220 is a radioactive gas with a half-life of 55.6 s. It has been identified as a possible health concern in specific places such as monazite processing plants and (rare-earth) mines. The short half-life of Rn-220 makes Rn-220 calibration sources and chambers less common than for the isotope Rn-222. There are many Rn-220 standard sources and chambers that are widely described in the literature and used for different applications and calibration. However, some of these chambers and sources are not easy to set up in typical nuclear environmental laboratories. In this project, we developed a Rn-220 standard source using a thorium nitrate solution (Th(NO3)4.6H2O). The solution was split into a large volume which was used in a Marinelli beaker to characterize its strength using a Hyper Pure Germanium (HPGe) detector, and a smaller volume of around 30 ml which was poured into a small bottle. The Rn-220 is extracted by bubbling air through the solution in the small bottle using an aerator. Gamma rays from the solution were measured simultaneously using a 76.2 mm × 76.2 mm NaI(Tl) detector. The gamma rays were measured for 66 hours. The accumulated spectra were thereafter analysed using an Excel spreadsheet where the counts in the Tl-208(2614 keV) peak were extracted and used to obtain the percentage of Rn-220 pumped out of the solution in the small bottle.Item Exploration of several radiation-based analytical techniques to investigate chlorides and chlorides effects within concrete(2007) Radebe, Mabuti Jacob; de Beer, F. C.; Lindsay, R.In this study, the capabilities of Neutron Radiography (NRad) and -Tomography (NTomo), as well as X-ray Radiography (XRad) to investigate chlorides and chlorides corrosion effects within steel reinforced laboratory concrete samples are practically explored. Capabilities of Scanning Electron Microscopy (SEM), Prompt Gamma Neutron Activation Analysis (PGNAA), Particle Induced X-ray Emission (PIXE), Small-Angle Neutron Scattering (SANS), Neutron Diffraction (NDIFF) and X-ray Diffraction (XDIFF) analytical techniques are also explored through review of literature.Item Gamma spectroscopy and lifetime measurements in the doubly-odd 194tl nucleus, revealing possible chiral symmetry breaking(University of the Western Cape, 2013) Masiteng, Paulus Lukisi; Lawrie, E. A.; Lindsay, R.In the first experiment high spin states in 194Tl, excited through the 181Ta (18O, 5n) heavyion fusion evaporation reaction were studied using the AFRODITE array at iThemba LABS. The γ-γ coincidences, RAD ratios and linear polarization measurements were carried out and the previously known level scheme of 194Tl was significantly extended. A total of five rotational bands four of which are new were observed. A pair of rotational bands associated with the πh9/2 ⊗ νi−1 13/2 configuration at lower spins and with the πh9/2 ⊗ νi−3 13/2 configuration at higher spins was found and interpreted as the first possible chiral bands followed above the band crossing. The two 4-quasiparticle bands show exceptionally close near-degeneracy in the excitation energies. Furthermore close similarity is also found in their alignments and B(M1)/B(E2) reduced transition probability ratios. In the second experiment lifetimes in 194Tl were measured using the DSAM technique with the excited states in this nucleus populated through the 181Ta (18O, 5n) reaction. A total of 25 lifetimes and 30 reduced transition probabilities of magnetic dipole B(M1) and electric quadrupole B(E2) have been evaluated. Furthermore B(M1) and B(E2) reduced transition probabilities in Bands 1 and 4, which have been regarded as chiral candidates, were found to be close to each other and reveals strong splitting along spin values. This further supports the proposed chiral nature of these two bands.Item Gamma spectroscopy of the doubly– ODD 194Tl Nucleus(University of the Western Cape, 2006) Ramashidzha, Tshifhiwa Marius; Gueorguieva, E. A.; Lindsay, R.; Dept. of Physics; Faculty of ScienceThe odd – odd Tl nuclei with A ≥ 190 have moderate oblate nuclear deformation and show rotational bands built on different quasiparticle excitations. Several phenomena, not yet fully understood, were observed in these nuclei, such as large signature splitting in the yrast band (built on a πh9/2⊗νi13/2 configuration), possible non – axiality of the nuclear shape, etc. In this work the high – spin states in 194Tl were studied. The 194Tl nuclei were produced in the 181Ta (18O, 5n) 194Tl reaction at a beam energy of 93 MeV and the γ - rays were detected using the AFRODITE array. The obtained extended level scheme of 194Tl is presented and discussed in this work. CSM (Cranking shell model) and TRS (Total Routhians Surface) models were both applied to interpret the results for band 1. The results were compared with the neighboring isotone 193Hg.Item In-situ measurements of radon concentrations in soil gas at a site on the Cape Flats(University of the Western Cape, 2007) Manavhela, Ramudzuli Fijiant; Lindsay, R.; Dept. of Physics; Faculty of ScienceMeasurements of radon (222Rn) concentration in soil gas are routinely used to locate geological fault zones. This study was undertaken to investigate the systematic effects that influence radon soil-gas measurements, in preparation for the first such fault zone measurements in South Africa. The measurements were made at two zones (called A and B for ease of reference) on the iThemba LABS site, which is located in Faure, on the Cape Flats, Western Cape (South Africa). There are no known faults located in the vicinity (~ 10 km) of the site. The radon measurements were made using a RAD7 (Durridge) radon monitor, which makes use of alpha spectrometry. A steel soil probe, which is inserted into the soil, was used to transfer radon from a certain depth in the soil to the RAD7 monitor via a flexible tube. Measurements were made at five sampling areas (three in zone A (A1, A2 and A3) and two in zone B (B1 and B2)), on the site during the months of May, August and October 2006. The variation of soilgas radon concentration as a function of depth, time of day and meteorological data were studied. The depths at which measurements were made were generally 25, 50, 75 and 100 cm. (In August and October, some of the depths were not considered due to a high water table.) Atmospheric temperature, air humidity, wind speed and atmospheric pressure were measured using a portable weather tracker (Kestrel 4000). The highest radon concentrations recorded were 11000 ± 776 Bq.m-3 and 26900 ±1370 Bq.m-3 at a depth of 100 cm in zone A and B, respectively (May). Generally, the radon concentrations were significantly quenched during the August and October measurements relative to the May values. The May soil-gas radon concentration profiles as a function of depth were fitted using a chi-square minimization procedure in order to extract diffusion lengths. A functional form derived from a onedimensional diffusion model was used for the fitting. One the parameter of the fit function is the 226Ra activity concentration. This was determined by means of gammaray spectrometry (in-situ and laboratory-based). A MEDUSA-type detector system comprising a CsI(Na) scintillator crystal and a GPS signal receiver were used for the in-situ measurements. A high-purity germanium detector (2.6 keV FWHM resolution at 1.33 MeV, 45 % relative efficiency) was used for the laboratory measurements. Significant seasonal variations in soil-gas radon concentration were observed (concentrations were generally much lower during or after the rainy season due to the presence of a high water table, and possibly the presence of more lush vegetation causing more radon to escape to the atmosphere). Significant (up to a factor of 2) local variation in radon concentration was observed at a particular depth, in a particular zone during autumn (just after the dry season). The soil-gas radon concentrations (for depth > 25 cm) in zone B were ~ factor of 2 higher than in zone A. The difference is largely due to the fact that the 226Ra soil activity concentrations in zone B were higher than in zone A (by a factor of ~ 1.6). Significant correlations (with coefficients > 0.6) were found between soil-gas radon concentrations and soil 226Ra activity concentrations (using a combination of zone A and B data). No significant, robust correlations (with correlation coefficients > 0.6) were found between soil-gas radon concentrations and meteorological parameters. Often contradictory results (in terms of the sign of the coefficient) were found. From measurements made at two depths (25 and 50 cm) in zone A, over a 24 hour period, there is evidence of a statistically significant variation between night and day radon concentrations, with the former being higher. The one-dimensional diffusion model used to fit the measured radon concentration depth profiles failed to fit the data when the results for a depth of 25 cm were included. When the 25 cm data were excluded the fits yielded diffusion lengths that are more realistic, although significant variations in diffusion length were found in a particular zone.Item Modelling and measurement of radon diffusion through soil for application on mine tailings dam(University of the Western Cape, 2004) Speelman, Wilcot John; Lindsay, R.; Dept. of Physics; Faculty of ScienceRadon has been identified as an important factor that could result in a health hazard by studies all around the world. The health risks can be minimised by preventive measures where radon is highly concentrated as in some mines and homes. Measuring and modelling the radon concentrations in the mine dump soil, can help to deduce the radon flux to identify the problem areas for rehabilitation especially in the cases of gold and uranium mine tailings. Rehabilitation in those cases usually consists of a multilayer cover of solids like crushed rock or clay. A passive method incorporating electret technology was used in this study to determine the radon emanation coefficient of the soil. This investigation also describes the modelling of a depth profile with respect to the radon activity concentration to understand from how deep radon might be migrating, as well as the effect of different diffusion lengths.Item Modern African nuclear detector laboratory: Development of state-of-the-art in-house detector facility at the University of the Western Cape(SpringerLink, 2021) Kapoor, K.; Orce, J.N; Abrahams, K; Akakpo, E; Bester, Z; Jenkins, D.G; Jordaan, K.L; Jones, M.Y.; Kamedien, M.A.; Lindsay, R.; Lomberg, B; Masango, S.; Ngwetsheni, C.; Ntshangase, S.S.; Radebe, N.; Triambak, S; Zyl, J.J. van,The upcoming detector facility aims at developing new state-of-the-art particle detectors as well as providing hands-on training to postgraduate students using both analog and digital signal processing from nuclear radiation detectors. The project is two-fold and aims at developing: 1) ancillary detectors to be coupled with the new GAMKA array at iThemba LABS. Of particular interest to our group is the determination of nuclear shapes, which depend on the hyperfine splitting of magnetic substates; 2) PET scanners for cancer imaging using a cheaper technology. Performance of NaI(Tl) inorganic scintillator detectors has been evaluated using PIXIE-16 modules from XIA digital electronics. Gamma-ray energy spectra were acquired from 60Co and 137Cs radioactive sources to calculate the detector resolution as well as to optimize the digital parameters. The present study focuses on improving and optimizing the slow and fast filter parameters for NaI(Tl) detectors which can eventually be used in the list mode of data aquisition.Item Production of Li, Be and B nuclei in the interaction of 12C with 12C at incident energies of 200 and 400 MeV(University of the Western Cape, 2008) Mira, Joele Paulus; Förtsch, S.V.; Lindsay, R.; Dept. of Physics; Faculty of ScienceThe objective of this project is to study the production of Li, Be and B isotopes emitted in the interaction of 12C with 12C at incident energies of 200 and 400 MeV.The energies of these produced fragments were measured with a detector telescope consisting of two silicon detectors at the incident energy of 200 MeV while a third silicon detector was added for the measurements at 400 MeV.Item Radiometric study of soil: the systematic effects(University of the Western Cape, 2007) Joseph, Angelo Daniel; Lindsay, R.; Newman, R.T.; Dept. of Physics; Faculty of ScienceThe natural 238U, 232Th and 40K radioactive content of vineyard soil was measured with an in-situ gamma-ray detector. The activity concentrations measured with the in-situ detector are normalized using the laboratory-determined activity concentrations of several samples from the vineyard site. To determine the activity concentration of a particular soil sample, the gamma-ray photopeak detection efficiencies are required. In this work, the detection efficiencies were derived for each soil sample using gamma-ray photopeaks associated with the radionuclides of 238U and 232Th present in the sample, and the 40K, 1460.8 keV gamma-ray peak, from KCl salt. The systematic effects related to the gamma ray photopeaks used, the sample moisture and sealing, sample volume or filling height, and sample density, were determined and applied in order to obtain the accurate sample activity concentrations. Assessment of the effect of using specific gamma photopeaks on the activity concentrations was done to confirm that the gamma-ray photopeaks highly prone to coincidence summing were omitted from the efficiency analysis. The effect of sample moisture and sealing suggested that in order to optimize the accuracy of each radioactivity measurement each sample must be oven dried and then hermitically sealed. The effect of volume or filling height variations of 0.47 % per mm between the sample and KCl standard was derived and this figure was incorporated into the uncertainty in each of the sample activity concentrations. The effect of density variations of less than 5 %, for sample densities ranging from 0.7 g.cm-3 to 1.6 g.cm-3, was determined and incorporated in the efficiency analysis and activity concentration uncertainties. After taking into account all these systematic effects, the soil sample activity concentration uncertainty was found to be no more than 10.4 % at the 95 % confidence level.Item Radon-222 measurements at Cape Point: A characterization of a 15-year time series(National Association for Clean Air, 2018) Botha, R.; Labuschagne, C.; Williams, A.G.; Bosman, G.; Brunke, E.-G.; Rossouw, A.; Lindsay, R.The Cape Point (CPT) Global Atmosphere Watch (GAW) research station have been monitoring climatically significant trace gases for four decades. Among these is radon, a naturally occurring noble gas with a large continental source, which has proven very useful for atmospheric tracer studies. 222Rn, the radioactive decay daughter product of radon gas, forms part of the long-term exposure of radiation dosages that humans are continuously exposed to in the environment. In a first of its kind for the African continent, a radon climatology, based on a 15-year measurement record at CPT, was published in the Atmospheric Environment journal (www.elsevier.com/locate/ atmosenv).Item Signature splitting and inversion in the 186-194 Au Nuclei predicted by the total routhian surface (TRS) and cranked shell model (CSM) calculations(University of the Western Cape, 2007) Shirinda, Obed; Gueorguieva, E. A.; Lindsay, R.; Dept. of Physics; Faculty of ScienceThe nearly oblate deformed Au nuclei show rotational bands built on multi quasiparticle excitations [Bou89, Bou92, Gue03, Gue01, Ven92]. Several of these bands are built on rotationally aligned high-j proton and neutron excitations. In many cases bands consisting of two or three signature partner E2 sequences are observed. For some fo these bands signature inversion is found and this feature gives a great challenge to the theoretical models. In this study the researcher performed TRS and CSM calculations for all high-j rotational bands in the p186-194s Au nuclei aiming to predict the signature splitting and inversion phemomena, alignments, gains in alignments, gains in alignment and band crossing frequencies observed.Item Spectroscopy of states in Ba 136 using the Ba 138 (p,t) reaction(American Physical Society, 2021) Rebeiro, B.M.; Triambak, S.; Garrett, P.E.; Lindsay, R.Background: The Ba136 isotope is the daughter nucleus in Xe136ββ decay. It also lies in a shape transitional region of the nuclear chart, making it a suitable candidate to test a variety of nuclear models. Purpose: To obtain spectroscopic information on states in Ba136, which will allow a better understanding of its low-lying structure. These data may prove useful to constrain future Xe136→Ba136 neutrinoless ββ decay matrix element calculations. Methods: A Ba138(p,t) reaction was used to populate states in Ba136 up to approximately 4.6 MeV in excitation energy. The tritons were detected using a high-resolution Q3D magnetic spectrograph. A distorted wave Born approximation analysis was performed for the measured triton angular distributions. Results: 102 excited states in Ba136 were observed, out of which 52 are reported for the first time. Definite spin-parity assignments are made for 26 newly observed states, while previously ambiguous assignments for ten other states are resolved. Together with other available data, the results are used to determine level densities in Ba136. These were compared with theory predictions, obtained using shell model calculations with Hamiltonians previously used for Xe136 neutrinoless ββ decay matrix element evaluations. Conclusions: The shell model predicted level densities agree reasonably well for the two Hamiltonians. However, the results for theory and experiment are found to agree only at lower energies, diverging from one another for the higher lying states, with the discrepancy increasing with energy. This is presumably because of lower production cross-sections for a majority of the higher-lying predicted states and the experimental limitations in resolving a large number of nearly degenerate states predicted by the theory. © 2021 American Physical Society.Item Studying chirality in a ~ 100, 130 and 190 mass regions(University of the Western Cape, 2011) Shirinda, Obed; Lawrie, E. A.; Lindsay, R.; Dept. of Physics; Faculty of ScienceChirality is a nuclear symmetry which is suggested to occur in nuclei when the total angular momentum of the system has an aplanar orientation [Fra97, Fra01]. It can occur for nuclei with triaxial shape, which have valence protons and neutrons with predominantly particle and hole nature. It is expected that the angular momenta of an odd particle and an odd hole (both occupying high-j orbitals) are aligned predominantly along the short and the long axes of the nucleus respectively, whereas the collective rotation occurs predominantly around the intermediate axis of a triaxially deformed nucleus in order to minimize the total energy of the system. Such symmetry is expected to be exhibited by a pair of degenerate DI = 1 rotational bands, i.e. all properties of the partner bands should be identical. The results suggested that spin independence of the energy staggering parameter S(I ) within two-quasiparticle chiral bands (previously suggested a fingerprint of chirality) is found only if the Coriolis interaction can be completely neglected. However, if the configuration is nonrestricted, the Coriolis interaction is often strong enough to create considerable energy staggering. It was also found that staggering in the intra- and inter-band B(M1) reduced transition probabilities (proposed as another fingerprint of chirality) may be a result of effects other than strongly broken chirality. Therefore, the use of the B(M1) staggering as a fingerprint of strongly broken chiral symmetry seems rather risky, in particular if the phase of the staggering is not checked.